Label mapping

Following a recent attempt to train a tagger on the 12-class behavior classification (run_strong, run_weak, cast_strong, cast_weak, etc), we would like to have the possibility to map the labels, in this particular case onto the 7-class behavior classification with rules such as run_strong => run_large, run_weak => small_motion, cast_weak => small_motion, etc.

This functionality could be specified in MaggotUBA's clf_config.json file similarly to feature #62.